Researchers working off the Shimokita Peninsula in Japan have discovered living microbes buried 8,000 feet below the seabed, a new record. And because they resemble those found in forest soils, these organisms likely survived for tens of millions of years after being buried under the seabed.

“Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained,” write the researchers in the abstract of their new study, which now appears at the journal Science. “Here we provide evidence for the existence of microbial communities in ~40° to 60°C [~104 to 140°F] sediment associated with lignite coal beds at ~1.5 to 2.5 km [~0.93 to 155 miles] below the seafloor in the Pacific Ocean off Japan.”

Microbes have never been discovered at depths this deep, where the pressure and heat are intense. Prior to this investigation, the previous record was 1,922 meters (6,305 feet).

After pulling up samples with drills—and ensuring contamination didn’t happen—the microbes were put through a genetic analysis. Researchers from the Japan Agency for Marine-Earth Science and Technology in Yokosuka, along with help from biogeochemists at the University of Bremen in Germany, found that a cubic centimeter of sediment contained about 10 to 10,000 microbial cells, which isn’t a whole lot. Typically, a soil sample contains billions of microorganisms. There’s obviously preciously little life at these depths—but there’s life nonetheless. As a researcher not involved with the study noted, “It’s like going to to Pluto and seeing McDonald’s.”

To find out more about what the microbes in the cores are like, the scientists compared their gene sequences with gene sequences of microorganisms living in other habitats. The microbial groups from far below the ocean floor differed from those in shallower layers. To the researchers’ surprise, the deep-sea microbes were more similar to modern microbes that live in forest soil. Thus the types of microbes that lived in the habitat 20 million years ago had a big influence on what microbes live there now...

It is possible that the microbes the team found are the descendants of terrestrial microorganisms that adapted to life under the sea as their home sank below the surface. But it’s also possible that these microorganisms are the same cells that were alive when the habitat began to sink, meaning they are more than 20 million years old. “We don’t know exactly the turnover rate of cells” in this environment, [co-author Fumio] Inagaki says.

Advertisement

Indeed, these organisms could provide a glimpse of what terrestrial life was like tens of millions of years ago. The microbes, which were found on a coal-bed below the seafloor, likely survived by extracting energy from coal and hydrogen. Their metabolisms may be running at very low levels, but they’re alive and well—even after their original environment was pushed underground more than 20 million years ago.